"Because it's alive, we don't recommend that we give it to people with compromised immune systems," said Dr. Fred Lopez, an infectious-disease specialist at LSU Health Sciences Center.

Pregnant women are in this category, he said, as are transplant recipients and people with diseases such as AIDS and cancer, as well as those with chronic conditions such as high blood pressure and diabetes.

The nasal spray, which is recommended for healthy 2- to 49-year-olds, "is a safe virus vaccine, provided you have an intact immune system, " Lopez said.

But the next shipment of "tens of thousands" of doses, which are expected to arrive late next week, will comprise injectable vaccines containing killed viruses that cannot cause disease, said René Milligan, a spokesman for the state Department of Health and Hospitals.

The nasal spray contains live virus because it can trigger a vigorous immune response along the respiratory tract, where the flu virus can enter the body.

In both forms, the new vaccine acts like the vaccine for seasonal flu: It is designed to stimulate the immune system to produce antibodies against the H1N1 virus. This process generally requires 12 to 15 days.

Wednesday's deliveries of 26,000 doses to doctors around the state are the first in a series of shipments that will arrive every few days, Milligan said.

"Hundreds of thousands" of doses will available by the end of the month, he said.

The nasal-spray vaccines aren't recommended for anyone younger than 2 because there are no data showing how children that young react to it, said Dr. Rodolfo Begué, Children's Hospital's director of infectious diseases.

The spray hasn't been properly tested in that age group, he said, because it's not practical to expect that anyone that young would put up with the procedure.

The injectable version is recommended for anyone at least 6 months old. Again, Begué said, there are no data showing how it would affect younger infants.

The vaccine is available with and without the preservative thimerosal, which, Begué said, has been controversial because it contains mercury, a fact that has made people fret about possible consequences, especially in young children with developing systems.

Such links have "never been proven, " he said. "Still, a lot of people prefer injections without thimerosal."

As the doses are sent out to Louisiana doctors who signed up to receive them, a list of those physicians will be available at www.fighttheflula.com, DHH spokesman Sean Smith said.

The H1N1 vaccine, which the federal Food and Drug Administration approved Sept. 15, is similar to the vaccine for seasonal influenza, Begué said.

Except for the warning about the potential threat of the nasal-spray vaccine, the H1N1 immunization is not expected to pose problems to people who get season flu shots each year, he said.

The first detection of the H1N1 virus in the United States was in April, and it has spread rapidly.

No exact case counts are available, not only because many people simply stay at home until they feel better but also because certifying cases takes time, including laboratory work, and doctors have been more concerned with treating symptoms without worrying about what type of flu they might be seeing.

Although Smith said there have been 1,300 confirmed cases in Louisiana, the health department estimates that as many as 79,000 have been infected.

There have been 14 deaths, including three announced Tuesday: a New Orleans area woman, a man from the Houma-Thibodaux area and a woman from the Lafayette area. Citing privacy reasons, the department has declined to release more information about them.

Nationally, according to the federal Centers for Disease Control and Prevention, 25,253 people have been hospitalized for treatment of H1N1 infections, and 1,972 people have died of this strain of flu and its complications, which can include pneumonia.